Field of the Disclosure
The present invention relates generally to input signal detecting circuits, and more specifically to circuits for detecting the shape of the input signal.
Background
Electronic devices use power to operate. Switched mode power converters are commonly used due to their high efficiency, small size and low weight to power many of today's electronics. Conventional wall sockets provide a high voltage alternating current. In a switching power converter a high voltage alternating current (ac) input is converted to provide a well-regulated direct current (dc) output through an energy transfer element to a load. In operation, a switch is utilized to provide the desired output by varying the duty cycle (typically the ratio of the ON time of the switch to the total switching period), varying the switching frequency or varying the number of pulses per unit time of the switch in a switched mode power converter.
The switched mode power converter also includes a controller. Output regulation may be achieved by sensing and controlling the output by employing a closed loop feedback topology. The controller may receive a signal representative of the output and the controller varies one or more parameters in response to the signal to regulate the output to a desired target. Properties, such as efficiency, size, weight and cost are usually taken into account when designing a switched mode power converter. The controller may also be designed to sense and respond to an input signal, such as an input voltage source.
For example, the controller may sense and respond to any input signal when the controller provides power factor correction (PFC) to improve the power factor of the power converter. Power factor may be defined as the ratio of the average power over a cycle to the product of the root mean square (rms) voltage and the rms current. In other words, the power factor may represent the ratio of the amount of usable power to the amount of total power delivered to the load. As such, the power factor may have a value between zero and one, with unity power factor being the ideal. A controller of a switched mode power converter may sense the input signal and perform PFC in an attempt to achieve unity power factor, typically by shaping the input current waveform as closely as possible to the input voltage waveform.
Corresponding reference characters indicate corresponding components throughout the several views of the drawings. Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention.